Cleaning up Eta Carinae: Detection of Ammonia in the Homunculus

Nathan Smith (1), Kate J. Brooks (2), Baerbel S. Koribalski (2), and John Bally (1)

(1) U. Colorado, (2) ATNF

We report the first detection of ammonia in the Homunculus nebula
around $\eta$ Carinae, which is also the first detection of emission
from a polyatomic molecule in this or any other luminous blue variable
(LBV) nebula. Observations of the NH$_3$ (J,K)=(3,3) inversion
transition made with the Australia Telescope Compact Array reveal
emission at locations where infrared H$_2$ emission had been detected
previously, near the strongest dust emission in the core of the
Homunculus. We also detect ammonia emission from the so-called
``strontium filament'' in the equatorial disk. The presence of NH$_3$
around $\eta$~Car hints that molecular shells around some Wolf-Rayet
stars could have originated in prior LBV eruptions, rather than in
cool red supergiant winds or the ambient interstellar medium.
Combined with the lack of any CO detection, NH$_3$ seems to suggest
that the Homunculus is nitrogen rich like the ionized ejecta around
$\eta$~Car. It also indicates that the Homunculus is a unique
laboratory in which to study unusual molecule and dust chemistry, as
well as their rapid formation in a nitrogen-rich environment around a
hot star. We encourage future observations of other transitions like
NH$_3$ (1,1) and (2,2), related molecules like N$_2$H$^+$, and renewed
attempts to detect CO.

Reference: 2006, ApJ, 645, L41
Status: Manuscript has been accepted